In systems and devices implementing near field communication (NFC), an NFC reader/writer device may communicate with several NFC enabled cards/tags. Such NFC cards/tags may be passive, meaning that they have no power. In a typical implementation, the coupling between the passive NFC cards/tags and the NFC reader/writer device may power up the NFC cards/tags to perform an NFC transaction or communications.
As a particular distance and/or orientation (i.e., during coupling) of the NFC card/tag varies with respect to the NFC reader/writer device, an effective impedance or antenna loading at an antenna of the NFC reader/writer device antenna may also vary. Because the modulation index, for example, is dependent on the effective impedance or impedance loading of the antenna, then the modulation index may vary as a function of the NFC tag/card position, orientation, and/or electrical characteristics.
Given the additional radio frequency (RF) circuitry between the antenna and an NFC module of the NFC reader/writer device, the varying impedance loading at the antenna front end may not accurately reflect the modulation index and other modulation characteristics that are implemented at the NFC module. Previous solutions either suffer this inaccuracy when measured at a NFC reader/writer output pins (i.e., NFC module). When measurement is directly performed at the antenna, an additional antenna lead connection may be needed. As such, there is a need to provide a solution that addresses may the problem of an additional antenna lead connection to obtain the measurement of the modulation characteristics at the antenna of the NFC reader/writer device.